Private Sub DrawControlborder(ByVal parent As Control, _
   ByVal bordercolor As Color)
 
   For Each ctl As Control In parent.Controls
 
      DrawControlborder(ctl, bordercolor)
 
      If ctl.Parent IsNot Nothing AndAlso (ctl.Visible And ctl.Enabled) Then
         Using g As Drawing.Graphics = _
         Drawing.Graphics.FromHwnd(ctl.Parent.Handle)
 
           Dim rect As New Rectangle(ctl.Location, ctl.Size)
           rect.X -= 2 : rect.Y -= 2 : rect.Width += 4 : rect.Height += 4
 
           Dim c As System.Drawing.Color
           If bordercolor = Color.Transparent Then
              c = ctl.Parent.BackColor 'Hintergrundfarbe des Parent
           Else
              c = bordercolor
           End If
 
           ControlPaint.DrawBorder(g, rect, c, ButtonBorderStyle.Solid)
         End Using
      End If
   Next ctl
End Sub

    If gDrawborder Then
       DrawControlborder(Me, Color.Red)
    Else
       DrawControlborder(Me, Color.Transparent)
    End If